1. Field of Invention
The present invention relates to a process using radiofrequency microwave energy to decompose hazardous matter and if necessary further oxidize them to environmentally safe residues.
2. Background
Wet air oxidation (WAO), a common subcategory of wet oxidation, is the oxidation of chemical substances that often represent hazardous materials whereby the oxidation products are of a nonhazardous nature. Generally such chemicals are organic substances, matter or materials, often referred to just as organics, and often represent a constituent of contaminated water. WAO is a common method of treating hazardous organic materials when they are in solution form; however, WAO also requires elevated temperatures and pressures. Characteristic temperatures employed are from 150-325.degree. C. while pressures are typically in the range of 2000-20,000 kPa. In most WAO processes agitation is employed to transfer oxygen from the gas phase to the liquid phase where the oxidation reaction occurs at these elevated conditions. U.S. patent application Ser. No. 09/064,266, filed Apr. 22, 1998 now U.S. Pat. No. 6,045,663 by Chang Yul Cha, entitled "Process for Microwave Enhancement of Wet Oxidation" describes microwave improvements in WAO, and its specification is hereby incorporated by reference.
In the subject case the oxidation of hazardous waste matter is chemically exemplified by hydrazine and its derivatives, monomethyl hydrazine (MMH) and unsymmetrical dimethyl hydrazine (UDMH), and is a primary consideration since they are examples of typical hazardous matter that are either water-borne or gas-borne. Unless otherwise indicated when the word "hydrazine" is employed it also includes its associated derivatives "MMH" and "UDMH".
Hydrazine is a common spacecraft propellant for use in missiles, rockets, and space launch vehicles. When used as such an astronautics fuel, nitrogen tetroxide is the most common oxidizer. However around space launch areas, much waste, both water and gases, containing dilute hydrazine occurs and must be environmentally processed. The subject invention performs microwave enhanced decomposition with further oxidation to environmentally acceptable gases and is a favorable process to perform this clean up task.
Another class of hazardous matter is microorganisms, which in general are water-borne although in the case of terrorists or accident situations, they are also potentially air-borne. The common water treatment for microorganisms is the use of chlorination although other treatments such as chloramination, chorine dioxide, ozonation, and UV radiation are employed. For example, see Byrant, et al., Disinfection Alternatives For Safe Drinking Water, Van Norstrand Reinhold, N.Y., 1992.
In the subject invention, microorganisms are characterized by the psetidomonas bacteria since this is conveniently available for laboratory experiments.
Quantum radiofrequency (RF) physics is based upon the phenomenon of resonant interaction with matter of electromagnetic radiation in the microwave and RF regions since every atom or molecule can absorb, and thus radiate, electromagnetic waves of various wavelengths. The rotational and vibrational frequencies of the electrons represent the most important frequency range. The electromagnetic frequency spectrum is usually divided into ultrasonic, microwave, and optical regions. The microwave region is from 300 megahertz (MHz) to 300 gigahertz (GHz) and encompasses frequencies used for much communication equipment. For instance, refer to Cook, Microwave Principles and Systems, Prentice-Hall, 1986.
Often the term microwaves or microwave energy is applied to a broad range of radiofrequency energies particularly with respect to the common heating frequencies, 915 MHz and 2450 MHz. The former is often employed in industrial heating applications while the latter is the frequency of the common household microwave oven and therefore represents a good frequency to excite water molecules. In this writing the term "microwaves" is generally employed to represent "radiofrequency energies selected from the range of about 500 to 5000 MHz", since in a practical sense this total range is employable for the subject invention.
The absorption of microwaves by the energy bands, particularly the vibrational energy levels, of atoms or molecules results in the thermal activation of the nonplasma material and the excitation of valence electrons. The nonplasma nature of these interactions is important for a separate and distinct form of heating employs plasma formed by arc conditions at a high temperature, often more than 3000.degree. F., and at much reduced pressures or vacuum conditions. For instances refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Supplementary Volume, pages 599-608, Plasma Technology. In microwave technology, as applied in the subject invention, neither condition is present and therefore no plasmas are formed.
Microwaves lower the effective activation energy required for desirable chemical reactions since they can act locally on a microscopic scale by exciting electrons of a group of specific atoms in contrast to normal global heating which raises the bulk temperature. Further this microscopic interaction is favored by polar molecules whose electrons become easily locally excited leading to high chemical activity; however, nonpolar molecules adjacent to such polar molecules are also affected but at a reduced extent. An example is the heating of polar water molecules in a common household microwave oven where the container is of nonpolar material, that is, microwave-passing, and stays relatively cool.
In this sense microwaves are often referred to as a form of catalysis when applied to chemical reaction rates. For instance, refer to Kirk-Othmer, Encyclopedia of Chemical Technology, 3rd Edition, Volume 15, pages 494-517, Microwave Technology.
U.S. Pat. No. Inventor Year 5,269,892 Cha 1993 5,451,302 Cha 1995
Referring to the above list, Cha in '892 discloses char-gas oxide reactions, such as NO.sub.x decomposition, catalyzed by microwaves, but does not decompose general hazardous matter.
Cha in '302 discloses microwave catalysis of chemical reactions using waveguide liquid films but with no carbonaceous material. The concentration of phosphoric acid by removal of bound water and the release of carbon dioxide from pregnant solutions of monoethanolamine are shown. However the subject invention does not utilize such a waveguide liquid film which requires a microwave-passing substrate.